The invention relates to cyclonic separating apparatus. Particularly, but not exclusively, the invention relates to cyclonic separating apparatus for use in vacuum cleaners.
Cyclonic separating apparatus in which particulate material is separated from a fluid, usually a gas, by means of high centrifugal forces is known. Such apparatus comprises a tapering cyclone body having a fluid inlet located at the larger end of the cyclone body and arranged to introduce fluid to the interior surface of the cyclone body in a tangential manner. The smaller end of the cyclone body is surrounded by a collector or, alternatively, leads to a particulate material outlet. A fluid outlet in the form of a vortex finder is located centrally of the larger end of the cyclone body. In use, the fluid inlet introduces the fluid with the particulate material entrained therein to the interior of the cyclone body in a tangential manner. The taper of the cyclone body causes the fluid to be accelerated down the length of the cyclone body which causes the particulate matter to be separated from the fluid and to collect in the collector or, if appropriate, to exit the apparatus via the material outlet. The fluid forms a vortex generally along the longitudinal axis of the cyclone body and exits the apparatus via the vortex finder at the centre of the larger end of the cyclone body.
When the exiting fluid passes through the vortex finder, it is spinning with a high angular velocity. If the offtake conduit leading from the vortex finder is linear with respect to the vortex finder (ie. the conduit has a central axis which is continuous with the central axis of the vortex finder), then the outgoing fluid will continue to spin as it travels along the conduit but will, eventually, revert to linear flow and the kinetic energy of the fluid flow associated with the spinning movement will be lost, probably in the form of frictional losses. Some attempt has been made to recover some of the kinetic energy of the spinning exiting fluid by utilising tangential offtakes from the vortex finder. The offtake is positioned so as to be tangential to one side of the vortex finder so that the spinning fluid enters the offtake in a linear manner. Examples of tangential offtakes used in conjunction with cyclonic separators are shown and described in the paper entitled xe2x80x9cThe Use of Tangential Offtakes for Energy Savings in Process Industriesxe2x80x9d by T. O""Doherty, M. Biffin and N. Syred (Journal of Process Mechanical Enginering, Vol. 206, Page 99ff). The arrangements shown and described in this paper attempt to convert some of the kinetic energy of the fluid flow into pressure energy. However, the pressure recovery is not wholly successful. This is partly due to the fact that the fluid flow exiting the cyclonic separator is still required to follow a path which contains sharp changes in direction. In the paper referred to above, the tangential offtakes are each located within a horizontal plane which requires the axial velocity component of the exiting fluid to be turned through a 90xc2x0 angle in a short distance. This results in turbulent flow downstream of the vortex finder which leads to energy loss from the fluid.
One application of such separators is in vacuum cleaners in which dirt and dust particles are separated from an airflow within the vacuum cleaner so that, when dirty air is drawn into the cleaner, the dirt and dust particles are separated from the airflow and retained for disposal whilst clean air is expelled. Vacuum cleaners of this type are shown and described in various prior published patents, such as EP 0 042 723, EP 0 636 338 and EP 0 134 654. Recovery of a higher proportion of the kinetic energy of the fluid exiting the cyclonic separating apparatus would result in a vacuum cleaner having a higher efficiency and thus a better level of performance.
It is an object of the present invention to provide cyclonic separating apparatus in which a greater proportion of the kinetic energy of exiting fluid is recoverable. It is a further object of the present invention to provide cyclonic separating apparatus which, when incorporated into a vacuum cleaner, results in the vacuum cleaner performing with a higher efficiency and/or better performance.
The invention provides a cyclonic separating apparatus comprising a tapering cyclone having an axis, a larger end and a smaller end, a fluid inlet and a fluid outlet located at the larger end of the cyclone, the fluid outlet being located coaxially with the cyclone, and a tangential offtake conduit communication with the fluid outlet, wherein the distance, measured parallel to the axis, between the tangential offtake and the smaller end of the cyclone increases in the downstream direction of the tangential offtake conduit. Preferably, the tangential offtake conduit follows a substantially helical path downstream of the fluid outlet. Such an arrangement allows the fluid exiting the separating apparatus to be gradually turned through a required angle without imposing sharp changes of direction. This reduces the amount of turbelence induced in the fluid flow by virtue of the direction change and this in turn reduces energy loss through friction.
The invention provides cyclonic separating apparatus comprising a tapering cyclone having an axis, a larger end and a smaller end, a fluid inlet and a fluid outlet located at the larger end of the cyclone, the fluid outlet being located coaxially with the cyclone, and a tangential offtake conduit communicating with the fluid outlet, wherein the distance, measured parallel to the axis, between the tangential offtake and the smaller end of the cyclone increases in the downstream direction of the tangential offtake conduit. Preferably, the tangential offtake conduit follows a substantially helical path downstream of the fluid outlet. Such an arrangement allows the fluid exiting the separating apparatus to be gradually turned through a required angle without imposing sharp changes of direction. This reduces the amount of turbulence induced in the fluid flow by virtue of the direction change and this in turn reduces energy loss through friction.
The tangential offtake conduit preferably has a central axis which is inclined at an angle of between 35xc2x0 and 70xc2x0, preferably 60xc2x0, to the longitudinal axis of the cyclone body. This arrangement turns the exiting fluid through a required angle without significantly increasing the possibility of separation occurring as the fluid passes through the tangential offtake conduit. It also allows the kinetic energy of the spinning fluid to be recovered as pressure energy which in turn results in the provision of a highly efficient system for separation of particles from a fluid.
In a preferred embodiment, a centerbody is located in the fluid outlet, which consists of a vortex finder. The tangential offtake conduit then communicates with an annular chamber delimited on the outside by the fluid outlet and on the inside by the centerbody. The arrangement of an annular chamber around the centerbody ensures that all of the exiting air is aligned with the tangential offtake conduit so that the amount of turbulence introduced at the entrance to the tangential offtake conduit is kept to a minimum.